Dies for necking tube ends



March 29, 1955 A, w s'n ETAL 2,705,275

DIES FOR NECKING TUBE ENDS Filed March 17, 1954 FIG. I.

INVENTORS AXEL wssrm SVEN wesrm Attorneys United States Patent DIES FOR NECKING TUBE ENDS Axel Westin, Milwaukee, and Sven Westin, Elm Grove, Wis.

Application March 17, 1954, Serial No. 416,877

4 Claims. (Cl. 219-3) This invention relates to dies for necking tube ends, and more particularly to a die for forming a neck or trunnion on the end of a cylindrical workpiece.

The invention uses the general principles of tube-end forming shown in United States Letters Patent No. 2,309,561, issued to the present inventors on January 26, 1943. In that patent, a rotating tubular blank is fed longitudinally into a die cavity formed by a plurality of circumferentially spaced electrode dies. As the blank progresses into the die cavity and engages the dies, an electric current flows through the blank between the dies, and resistance of the blank to the flow of current creates a heating action which softens the end of the blank and causes it to take the general shape of the die cavity when longitudinal force is continuously applied.

Heretofore, in the manufacture of cylindrical blanks as described above, the die cavity has been shaped to provide an outer portion of substantially cylindrical shape and relatively large diameter which at its inner end merges into a cylindrical neck portion of smaller diameter ending in an abutment, the plane of which is perpendicular to the longitudinal axis of the dies. As the tubular blank was fed into these former dies and heated, the walls of the blank tended to follow the walls of the die cavity. However, it was found that as the end of the blank reached the abutment and longitudinal pressure continued to be applied to upset and thicken the walls of the workpiece in the neck portion, the walls of the blank tended to buckle or thicken inwardly in the area of the merging curve between the outer portion of the cavity and the smaller inner neck, hereinafter called the necking curve. Thus a uniform finished piece could not be assured.

Prior to this invention attempts to overcome buckling and uneven thickening of the blank as the end walls were upset have not been entirely satisfactory, even though a cam was often used to lessen the longitudinal pressure at this stage of the process.

The present invention is based on the discovery that a tapered portion on the inner end of the neck, which replaces the abutment used heretofore, will cushion the flow of the tubular blank after it has reached the extreme end of the die cavity, thereby substantially reducing buckling and uneven thickening in the area of the necking curve, while at the same time providing enough mechanical resistance to effect thickening of the walls of the neck. Longitudinal pressure variations are unnecessary, and a cam mechanism can be dispensed with for this step of the forming process.

The accompanying drawings illustrate the best mode presently contemplated by the inventor for carrying out the invention.

In the drawings:

Figure 1 is a side elevation of the apparatus incorporating our invention, with parts broken away and sectioned;

Fig. 2 is a central vertical longitudinal section of the dies, showing the blank in the process of being formed;

Fig. 3 is a transverse section taken on line 33 of Fl .2;

Tig. 4 is a view similar to Fig. 2 showing the completely formed tube being withdrawn from the dies;

Fig. 5 is a longitudinal cross section of the dies, showing another embodiment of our invention; and

Fig. 6 is a longitudinal cross section of the dies, showing still another embodiment of our invention.

As illustrated in the drawings, the forming apparatus Patented Mar. 29, 1955 comprises a plurality of adjacent electrode die members 1 and 2, which are connected by the corresponding lead-in wires 3 and 4 to the secondary of a transformer 5 supplied with a source of power from main line 6. Although only two die members are illustrated, three or more such members may be used if desired.

Die members 1 and 2 have a common die recess 7 comprising a relatively large circular mouth portion 8 which merges by appropriate curves into a narrow central cylindrical neck portion 9. The inner curve will hereinafter be designated as necking curve 10.

Month portion 8 is of suflicient diameter to receive the end of a tubular blank 11. It is preferable to use some sort of pre-heat-ing apparatus, such as that shown in Patent No. 2,322,444, issued to W. C. Heath on June 22, 1944, in order to avoid the necessity of providing a substantial axial extent for the mouth.

According to the invention, at the extreme inner end of die cavity 7 the walls of neck portion 9 are tapered at 12, as shown in Figures 1 through 4, which produces mechanical resistance to the longitudinal movement of the tubular blank 11.

Tapered portion 12 of neck 9 may constitute a mere tapered shoulder in the neck leaving the rear end of the neck open, as shown, or the tapered portion may substantially close the neck, if desired.

The degree of taper in portion 9 which will effect thickening of the neck Walls of the blank without buckling or uneven thickening of the adjacent walls will depend on many factors, such as: pre-heat, current, composition and thickness of the blank, speed of rotation of the blank, relative dimensions of the die cavity, etc.

In carrying out the invention, one end of tubular blank 11, which is supported at its opposite end by a rotatably mounted chuck 13, is fed longitudinally into die cavity 7. As the rotating blank 11 progresses into die cavity 7 and engages the dies, an electric current flows through the blank between die members 1 and 2, thereby resistance heating the portion of blank 11 to be formed. As longitudinal pressure continues to be applied, the heated walls of blank 11 progress inwardly of the dies and around necking curve 10 into narrow neck portion 9, as shown in Fig. 2.

Finally, the end of blank 11 reaches tapered portion 12 of neck 9. Continuing longitudinal pressure creates a mechanical resistance of snfiicient strength to upset and thicken the end walls of blank 11. This resistance is not sufficient, however, to cause the blank to buckle inwardly in the area of necking curve 10. The thickening has been found to be much more uniform than was heretofore possible.

It is preferable to cut the current off as blank 11 enters neck 9, it having been found that to continue the resistance heating action beyond that point tends to overheatthe end of blank 11 and injure the die members. The resistance heating action during the earlier part of the forming operation is sufficient to allow completion of the operation without the further use of electric current.

Longitudinal pressure may be applied continuously until neck 9 fills with metal from blank 11 but in most instances it is desirable to stop the operation while neck 9 is substantially hollow.

A small pin, somewhat similar to that shown in Patent No. 2,313,067, issued on March 9, 1943, to W. C. Heath, may be employed to keep the end of the tube open during the forming process.

A tapered pin 14 may be utilized at the end of neck portion 9, as shown in Figure 5. In this instance, the inner end portion of the die cavity need not be tapered, pin 14 serving to cushion the flow of blank 11 in a manner similar to the cushioning hereinbefore described.

If desired, the mechanical resistance may be provided by a spring-pressed abutment pin 15, as shown in Fig. 6. There need be no tapering of the neck portion of the die members if this type of pin is utilized, the spring providing gradually increasing mechanical resistance as the pin is pressed rearwardly by the end of the blank. This will serve to prevent buckling and uneven thickening in the area of necking curve 10.

A tubular air hole not shown, may be disposed within end of the pin with nooutlet at the forward end.

pins 14 or 15 for purposes of cooling the pin. This hole extends along the pins central axis and may run entirely through said pin, or it may be formed so as to run from the rearward end to a point near the forward In the latter case, a small hollow tube which is connected to an air supply is inserted into the hole, and air is passed through said tube. The air is emitted from the end of the tube and returns rearwardly between the outer walls of the tube and the walls of the hole.

Because mechanical resistance of tapered portion 12 replaces the heretofore used abutment, the neck walls of the blank may be thickened without danger of buckling or uneven thickening of the walls approaching the neck. The need for lessening of the longitudinal force to reduce the danger of injuring the blank is now dispensed with, due to the novel formation of the die cavitys extremity. Since high and relatively constant longitudinal pressure can be used, there is a great saving in time and a cam arrangement to vary the pressure is no longer needed for this stage of the forming process. After the blank is entirely formed, it is removed from the dies and the tapered portion of the neck may be out 01f or left on, as desired.

Various modes of carrying out the invention are contemplated as within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

We claim:

1. In an apparatus of the class described for necking tube ends, a plurality of electrode die members disposed in circumferentially spaced relation to form a die cavity therebetween having a circular mouth portion adapted to receive the end of the tube and merging rearwardly into a smaller central neck portion of substantially less diameter than said mouth portion, and a mechanical resistance in said neck portion to cushion the flow of metal therein and upset the same.

2. The apparatus of claim 1 in which the mechanical resistance comprises a tapered die portion in the rearward end of the neck which reduces the diameter of said neck.

3. The apparatus of claim 1 in which the mechanical resistance comprises a pin disposed in the rearward end of the neck and which is tapered to reduce the radial space between the pin and the neck portion of said die members in the direction of metal flow.

4. The apparatus of claim 1 in which the mechanical resistance comprises a spring pressed abutment pin disposed in the rearward end of the neck, said pin serving to provide a gradually increasing mechanical resistance to rearward motion of the tube.

References Cited in the file of this patent UNITED STATES PATENTS 

